I. Field of the Invention
This invention relates to a rotary cone seal with two or more elastomeric materials joined together to form the seal.
More particularly, this invention is a composite seal with two or more elastomeric materials bonded together with further means affixed to the seal to minimize damage to the seal from detritus invading the seal cavity surrounding the seal.
II. Description of the Prior Art
There are a number of prior art patents that teach seals for sealed bearing rotary cone rock bits.
For example, U.S. Pat. No. 3,765,495 describes an earth boring drill employing roller cone cutters with a seal to inhibit ingress of detritus into the cutter bearing area and egress of lubricant therefrom. The seal cavity and adjacent journal is designed to place the seal in hoop compression. The shape of the seal is such that its cross-section is not overly compressed or displaced when in operating position. The seal has a greater radial cross-sectional extent than axial extent by a ratio of at least one-and-one-half to one to conserve bearing space and to provide flexibility to accommodate the various movements of the cutter cone relative to its bearing journal which it is rotatively mounted.
Since the seal is fabricated from a homogeneous resilient material, the portion of the seal adjacent to the journal bearing is exposed to debris and thus, vulnerable to wear that will eventually compromise the seal. The seal, of necessity, has to be flexible enough to maintain the seal in hoop compression as heretofore mentioned. If the seal material is too hard in an attempt to resist abrasion it will not be resilient enough to maintain proper hoop compression.
U.S. Pat. No. 3,788,654 teaches a multiple hardness o-ring seal. A molded ring of partially activated nitrile rubber materials subsequently forms a hardened skin by the process of surface curing the inactivated materials in a solution of a curing agent. The nitrile rubber curing agent provides a secondary curing period which increases the exterior hardness of the seal. The compression set characteristics of the o-ring however are somewhat sacrificed as a result. Furthermore, the hardened skin does not necessarily provide lower friction and/or greater wear resistance.
The harsh environment sealed bearing rock bits are subjected to, demand that the bearing seals adapt to these conditions. For example, hard rock earthen formations subject the roller cone cutters to uneven loads that eventually cause the cones to eccentrically wobble on their respective journal bearings especially after extended run times. In addition, heat buildup caused from depth of bit penetration, weight on bit and relatively high bit rotational speeds challenge the seals to perform despite these deterring factors. Moreover, modern day drilling techniques have resulted in higher bit rotational speeds deeper borehole penetration depths and a greater weight on the bit that further challenges the performance of the rotary cone seals.
The prior art seals, while they exhibited adequate performance under ordinary drilling conditions, lack the necessary composition to withstand the higher performance demanded by drilling operators competing in the petroleum industry.
The present invention teaches the fabrication of a composite seal designed to resist abrasion from borehole detritus and heat from high rotary speeds. In addition, the seal is pliable enough to maintain a seal despite cone wobble and excessive bit weight.